1. Field of the Invention
This invention relates to an ion sensor for measuring the ionic concentration of a solution by the potentiometric response of an electrode. More particularly, the invention relates to a solid-state ion sensor devoid of an internal (standard) solution, especially an ion sensor capable of measuring ionic concentration in vivo.
2. Description of the Prior Art
An ion sensor most commonly used in the prior art is constituted by a glass membrane electrode. However, the glass membrane in such an electrode breaks easily, and frequent washing is necessary since measurements taken thereby are influenced by the existence of interfering ions, medicines, the proteins in a living body, amino acids and trace amounts of active ingredients. These and other inconveniences are encountered in terms of use.
Recently, pH electrodes using a polymeric membrane have recently been reported as an improvement on the glass membrane electrode. For example, a liquid membrane electrode is described in Analytical Chimica Acta, 131, (1981), pp. 111.congruent.116, and a solid membrane electrode is disclosed in Japanese Patent Application No. 59-281076. However, since these electrodes possess an internal liquid chamber just as the glass membrane electrode, they do not fundamentally solve the problems of the glass electrode and are not fully satisfactory.
However, ionic concentration measurements for clinical examinations and the like are now being performed under increasingly harsh conditions. In addition to the ability to perform measurements precisely, these sensors must have characteristics that (1) enable ionic concentration measurements to be performed continuously and (2) enable ionic concentration measurements to be performed accurately even if there is a sudden change in temperature.
Membrane-coated solid-state electrodes can be made very small. They also do not have an internal liquid chamber and, hence, there is no risk of an internal liquid leaking and contaminating a specimen undergoing measurement. For these reasons, electrodes of this type are attracting considerable interest since they are well-suited for use as clinical sensors.